1. Technical Field
The invention relates generally to downhole tools and methods for completing a well and, more particularly, to a downhole tool and method for placing a gravel pack in a well.
2. Background Art
In the petroleum industry, completion of a well drilled through subterranean formations generally involves lining the well with a casing and using a perforating gun to create perforation tunnels through the casing and the formation adjacent the casing. The perforation tunnels are usually created adjacent the formation at pay zones to allow reservoir fluids to flow from the formation into the well. During production of the reservoir fluids, sand may flow from the formation into the well if the formation is composed of unconsolidated sand. Typically, production of sand along with reservoir fluids is undesirable for many reasons, some of which include clogging of surface equipment, erosion of the tubing strings and wellhead, and bridging of the well such that further production of reservoir fluids is prevented.
However, production of sand along with reservoir sands is not a new problem in the petroleum industry, and there has been a lot of research and development in the area of sand control during reservoir fluid production. One sand control technique that has been found to be successful and reliable is gravel pack completion. Gravel pack completion involves placing a screen in the well adjacent the perforation tunnels and filling an annular area between the casing and the screen, as well as the perforation tunnels, with well-sorted, coarse sand, called gravel pack. The gravel pack is highly porous and permeable and serves to filter formation sand from the reservoir fluids entering the well. The filtering performance of the gravel pack depends on the size and shape of the gravel pack sand and how well the gravel pack fills the annular area between the casing and the screen. If there are voids in the gravel pack, the formation sand can fill the voids and reduce the rate at which the reservoir fluids are produced, or the produced sand can erode the screen and cause the gravel pack to fail.
One method for efficiently placing gravel pack in the well and the perforation tunnels is circulating gravel packing. A gravel pack tool is lowered into the well on the end of a tubing string and gravel suspended in a carrier fluid is pumped down the bore of the tubing string and through a crossover tool into the annular area between the screen and the casing. The gravel is held in place by the screen while the carrier fluid flows through the screen and crossover tool into the casing annulus and back to the surface. Generally, the gravel pack tool is substantially larger than the tubing string and would typically require that any existing tubing string and other restrictions in the well be removed before the gravel pack tool is run into the well. However, retrieval of existing tubing in a well is a relatively expensive operation and may not be economically viable for marginally producing or nearly depleted wells.
Another method for placing gravel pack in the well and the perforation tunnel involves pumping a gravel slurry in a viscous carrier fluid through a tubing string. The carrier fluid is squeezed into the formation and placed across the perforated interval. Again, while the tubing string may be lowered through an existing tubing in the well, the cost of deploying the tubing string may be fairly expensive for marginally producing wells. Thus, it would be beneficial to have a tool that can efficiently place a gravel pack in a well and that can be lowered into the well through a tubing and other restrictions in the well. U.S. Pat. Nos. 5,033,549 and 5,115,860 to Champeaux et al. disclose a gravel pack tool that can be lowered through a tubing on the end of an electric wireline. The gravel pack tool features radially extending members that collapse while the gravel pack tool is lowered through the tubing and extends when the gravel pack is placed below the tubing. Gravel is disposed in the well annulus using a dump bailer.